Manufacturing processes of pulp and paper often involve deposition of contaminants, including among others scales; pitch consisting of resin acids or fatty acids derived from wood or latex derived from coating layers; sticky contaminants derived from adhesive materials (acrylic, vinyl acetate, hot-melt and the like adhesive materials such as adhesive tapes, glues for binding magazines, plastic tapes, etc.) contained in waste paper; and chemicals such as sizing agents or starch added in the processes; and these contaminants adhere to wires, canvas, felt or the like to cause problems including decreased paper machine runnability such as dehydration failure or paper breaks and product quality loss such as paper surface defects.
These pitch and sticky contaminants are dispersed as very small particles or colloids in slurries during the papermaking process, but destabilized from the dispersed state by high shear stress, rapid pH change, addition of fixing agents such as aluminum sulfate or the like so that they are deposited or agglomerated/coalesced by binding to impurity ions or inorganic or organic matters. Coalesced pitch is deposited on pipes, wires or the like or redeposited on pulp or paper to cause quality loss due to defects in paper and paper breaks inducing productivity loss and the like.
Especially, the recent trends toward closed processes for environmental consideration have amplified and complicated pitch problems. Moreover, an increased use of recycled pulp for environmental consideration and cost saving has tended to introduce higher amounts of pitch or sticky contaminants into manufacturing processes of pulp and paper and worsened problems with these contaminants.
To address the problems with pitch or sticky contaminants described above, it is very important to know the numerical level or characteristics of the pitch or sticky contaminants introduced into manufacturing processes of pulp and paper, and some methods for evaluating pitch and coalesced sticky contaminants that can be eliminated by a screen having a slit width of 100 μm have been currently established and have been known to provide reliable data.
However, it is very difficult to evaluate small sticky contaminants due to their properties, and no method has been established though many reports exist. For example, an approach to evaluate small sticky contaminants relies on organic solvent extraction. However, this method determines the amounts of not only sticky contaminants but also oils derived from ink vehicles or other non-sticky solvent extracts derived from surfactants.
It cannot be said that the amounts of sticky contaminants are precisely determined by such an extraction method, as shown from the analytical results of adhesive-derived components occupying solvent extracts of deposits in an actual manufacturing process in non-patent document 1 reporting that adhesives represent only slightly less than about 5% of the extracts, for example. In addition, this method requires a very long time including extraction time (non-patent document 1).
Other methods have also been proposed by determining the amounts of deposits on a hydrophobic film or a metal wire, or determining COD or TOC or the like, but these methods are insufficient for determining small sticky contaminants because the amounts of deposits are very small so that the former method introduces a significant error from other materials such as fibers while the latter method fails to evaluate deposition by COD or TOC (non-patent documents 2 and 3).
Based on the recently evolved techniques for determining deposition of substances in water using a quartz crystal oscillator, methods for determining the degree of deposition of contaminants (patent document 1) and methods for monitoring deposition of organic or inorganic matters (patent documents 2 and 3) have been proposed. These methods allow accurate quantification of very small amounts so that the amounts of the pitch or small sticky contaminants deposited or sedimented can be precisely determined.